A network of a long term evolution (LTE) system put to practical use as a next-generation radio access system controls a congestion state of the network by an access barring method as illustrated in FIG. 8 (see Non-Patent Literature 1).
A concept of an access class (AC) is introduced to the network access barring method of the LTE. Each mobile device belongs to at least one AC, and in the AC, normal type ACs (AC=0 to 9) and special type ACs (AC=11 to 15) exist.
As the special type AC, for example, AC=11 is allocated to a mobile device for network operators, AC=12 is allocated to a mobile device for police services, AC=13 is allocated to a mobile device for use by government, and AC=14 is allocated to a mobile device for emergency services. The normal type AC may be additionally allocated to the mobile device to which the special type AC is allocated.
In access barring of the LTE, each AC notifies whether the AC is subject to no barring (0) or whether the AC is subject to barring (1) as information of ac-BarringForSpecialAC. Note that the normal type ACs (AC=0 to 9) cannot be subject to no barring (0) when the network requires some sort of barring. Therefore, only the information of the special type ACs (AC=11 to 15) needs to be notified.
That is, in the LTE system, information designating no barring (0) to preferential ACs (for example, AC=12 and 14) from among the special type ACs, and designating barring (1) to the rest of the special type ACs and the normal type ACs (for example, AC=0 to 9, 11, 13, and 15) is notified.
In the network access barring method of the LTE, while an access of at least a part of the ACs to which barring (1) is designated is denied, keeping an access of the same AC denied for a long time is problematic from a standpoint of fairness of communication service. Therefore, appropriateness of an access is determined by comparison with a random number generated by a mobile device so that a mobile device, an access of which is denied, is changed with time.
For example, when it is desired to bar 30%, if a value indicating “70%” is notified in advance, the mobile device compares the value and a random number, so that it is determined that an access is allowed by the probability of 70% (70% from among the mobile devices with barring, which have received barring information), and it is determined that an access is denied by the probability of 30% (30% from among the mobile devices with barring, which have received the barring information). Since each mobile device generates a random number every time accessing the network, it is determined that an access of any mobile device is allowed 7 times out of 10 on average from a mobile device's viewpoint, whereby the fairness is maintained.
For this purpose, in the LTE, information for designating values at 5% interval between 0 and 95% (values to be compared with a random number by a mobile device having an AC that is subject to barring) is notified as information of ac-BarringFactor.
Then, the mobile device that has received the barring information, as illustrated in FIG. 8, according to the ac-BarringForSpecialAC, proceeds to Yes at S910 regarding the ACs to which 0 is designated from among the special type ACs (for example, AC=12 and 14) and determines that an access is allowed (S950), and proceeds to No at S910 regarding the ACs to which 1 is designated from among the special type ACs and the normal type ACs (for example, AC=0 to 9, 11, 13, 15) and causes the ACs to generate random numbers (S920). If the generated random number is smaller than the value designated by the ac-BarringFactor (Yes at S930), it is determined that an access is allowed (S950), and if the generated random number is larger than the value designated by the ac-BarringFactor (No at S930), it is determined that an access is denied (S940).